The present disclosure broadly relates to the art of vehicle suspension systems and, more particularly, to a gas spring assembly suitable for use on a vehicle suspension system. The gas spring assembly includes a porous flow restrictor capable of maintaining laminar gas flow between two gas chambers that are interconnected by the porous flow restrictor.
Vehicle suspension systems typically include a plurality of spring elements for accommodating forces and loads associated with the operation and use of the vehicle. In such vehicle suspension system applications, it is often considered desirable to select spring elements that have the lowest suitable spring rate, as this favorably influences ride quality and comfort. That is, it is well understood in the art that the use of spring elements having higher spring rates (i.e., stiffer springs) will transmit a greater magnitude of road inputs into the sprung mass of the vehicle and that this typically results in a rougher, less-comfortable ride. Whereas, the use of spring elements having lower spring rates (i.e., softer, more-compliant springs) will transmit a lesser amount of the road inputs to the sprung mass and will, thus, provide a more comfortable ride.
With more specific reference to gas springs, it is possible to reduce the spring rate of gas springs, thereby improving ride comfort, by increasing the volume of pressurized gas operatively associated with the gas spring. This is commonly done by placing an additional chamber, cavity or volume filled with pressurized gas into fluid communication with the primary spring chamber of the gas spring, as is well known by those of skill in the art. Such additional volumes can be formed within a component of the gas spring itself, as shown, for example, in U.S. Pat. No. 5,954,316, or provided separately and connected through one or more passages, as shown, for example, in U.S. Pat. No. 6,691,989.
Vehicle suspension systems also commonly include a plurality of dampers or damping elements that are operative to dissipate undesired inputs and movements of the vehicle, particularly during dynamic operation thereof. Typically, such dampers are liquid filled and operatively connected between the sprung and unsprung masses of the vehicle. In other arrangements, however, the damping elements can be of a type and kind that utilize gaseous fluid rather than liquid as the working medium. In such known constructions, the gas damper portion permits gas flow between two or more volumes of pressurized gas, such as through one or more orifices, as shown, for example in U.S. Patent Application Publication No. 2004/0124571 A1, or through one or more valve ports, as shown, for example, in U.S. Patent Application Publication No. 2003/0173723. Generally, there is some resistance to the movement of pressurized gas through these passages or ports, and this resistance acts to dissipate energy associated with the gas spring portion and thereby provide some measure of damping.
Various disadvantages exist with known gas spring constructions that include additional gas volumes to assist in reducing the spring rate of the gas spring, and at least some of these disadvantages involve the movement of air between the two volumes. That is, the flow of pressurized gas between the two volumes is at least partially dependent upon the size, length, shape and number of fluid pathways connecting the two volumes. It will be appreciated that one or more, very large, fluid-communication pathways would permit increased quantities of pressurized gas to flow between the two volumes. However, such pathways would provide reduced resistance to gas flow and, thus, provide minimal damping characteristics. What's more, such very large pathways are often difficult to provide, given the limited operating and mounting envelopes normally associated with vehicle suspension systems.
Increased damping performance can, of course, be provided by reducing the size, increasing the length, altering the shape and/or reducing the number of fluid pathways between the two volumes. However, such alterations would normally provide increased damping performance at the expense of other performance characteristics of the gas spring. That is, the changes that increase the resistance to flow through the passages and, thus, increase damping performance will typically also decrease the effectiveness of the additional gas volume to reduce the spring rate of the gas spring. For example, such alterations can render a pathway more susceptible to choked flow conditions, during which gas flow through the passageway is substantially reduced or even stalled.
Another disadvantage of such known arrangements, is that a pathway, orifice or valve port of a given size is normally only capable of providing damping performance over a relatively small range of frequencies, such as from about ±2.5 Hz to about ±5 Hz. So, for an orifice that is sized to damp a nominal frequency of 10 Hz, a range of frequencies of from about 7.5 Hz to about 12.5 Hz or possibly a range of frequencies as wide as from about 5 Hz to about 15 Hz may be damped. Unfortunately, vibrations associated with the operation and use of a vehicle normally range from very low frequencies, such as from about 0.1 Hz to about 40 Hz, for example, as well as significantly higher frequencies, such as from about 40 Hz to about 100 Hz, for example. Thus, it is often desirable for a vehicle suspension system to attenuate vibrations within a wider range of frequencies, such as from about 0.1 Hz to about 100 Hz, for example, than is normally damped by a gas damper that simply uses one or more orifices. Unfortunately, known gas damping devices are generally incapable of attenuating such a wide range of frequencies of vibration.
Thus, it is desired to develop a gas spring assembly as well as a vehicle suspension system using the same that overcomes the foregoing and other problems and disadvantages associated with known constructions.